At the AFBI Hillsborough research farm near Hillsborough, south-east Northern Ireland (clay loam topsoil texture), direct N2O-N emissions were measured from replicated (x3) plots (4 x 12 m) arranged in a randomised block design. Dairy cattle slurry (30 m3/ha) was applied to permanent grassland in autumn (early-October) and spring (early-April). The cattle slurry was applied using watering cans simulating bandspreading and surface broadcast application, with slurry applied across the whole area of the plot for surface broadcast treatments and applied in bands spaced 20cm apart to simulate bandspread treatments.
In two separate treatments, the commercially available nitrification inhibitor - dicyandiamide (DCD) was applied by knapsack sprayer to the sward, within 1 hour of slurry application by surface broadcast and band spreading, to give a DCD application rate of 10 kg /ha (6.5 kg N/ha). An untreated control treatment was included where no slurry was applied.
Following slurry application, measurements of direct N2O-N were made over c.12 months, using 5 static chambers (0.8 m2 total surface area) per plot and analysed by gas chromatography. In a separate area of the plot, a wind tunnel technique was used (one per plot) to measure ammonia-N emissions for 7 days after each slurry application. Grass yields and N offtakes were measured following grass cuts in late-May, early-July and early-August 2013.
The County Down, 2012-13 manure experiment contains data sets of; annual nitrous oxide emissions, annual nitrous oxide emission factors, total ammonia loss, soil moisture, top soil mineral nitrogen (selected dates), temperature, rainfall and associated crop (grass yield and nitrogen offtakes) and soil measurements.

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Detailed nitrous oxide emission measurement methodology:
Direct N2O emissions were measured with five static flux chambers (40 cm wide x 40 cm long x 25 cm high) per plot, covering a total surface area of 0.8 m2. The chambers were stainless steel and un-vented. Adhesive-backed expanded neoprene, 6 mm thick, was inserted into the 3 cm diameter channel on the upper rim of each chamber base, and a 10 kg drum filled with water placed on top of the chamber lid, to ensure an air-tight seal formed following chamber closure (Smith et al., 2012). Chambers were pushed into the soil up to a depth of 5 cm and remained in place throughout the experiment, except during urine/dung application and grass cutting when chambers were removed, locations were marked, and chambers were re-instated to the same position as prior to removal.
Chambers remained open except for a short time on each sampling day. On that day, ten samples of ambient air were taken to represent time zero (T0) N2O samples. From each chamber, after a 40-minute enclosure period (T40) a headspace sample was taken using a 20-ml syringe and injected into a pre-evacuated, pre-labelled 12 ml Labco vial fitted with a double-wadded PTFE/silicone septum, which were over pressurised during storage. Immediately before Gas Chromatography (GC) analysis, vials were vented to atmospheric pressure by piercing the septa with a 25 gauge needle. The N2O flux was calculated using an assumed linear increase in N2O concentration from the ambient N2O concentration (T0) to the N2O concentration inside the chamber after 40-minutes enclosure (T40) (Chadwick et al., 2014). Throughout each experiment, the linearity of emissions through time was checked routinely from three chambers located on the treatment where cattle slurry had been surface broadcast applied. A minimum of seven samples were taken from each chamber at 10 min intervals commencing at closure i.e. T0, T10, T20, T30, T40, T50, T60. A duplicate sample was taken along with the linearity sample at T40.
In order to minimise the effect of diurnal variation, gas sampling was carried out between 10:00 am and 12:00 pm as referred to in the IPCC good practice guidance (IPCC, 2000). Gas samples were analysed as soon as possible after collection to minimise potential leakage (usually within 2 weeks of field measurements) using gas chromatographs fitted with an electron-capture detector and an automated sample injection system. Following receipt in the laboratory, six freshly prepared standards per sampling day (two replicates of each standard) were stored with the samples and were used to verify sample integrity during storage. The gas chromatographs were calibrated on a daily basis using certified N2O standard gas mixtures.
An exchange of samples of chamber air and standard gas mixtures between labs from the different research organisations involved in the InveN2Ory programme of experiments who operated the GCs were carried out, to avoid the possibility of any bias in the results towards high or low values.
Following manure application, N2O flux measurements were carried out in line with the following sampling schedule until either the next fertiliser application or the final application at the end of the monitoring period; measurements were taken on four occasions in the week of, and week after, fertiliser application, twice weekly for the next two weeks, every other week over the next c.four months, decreasing in frequency to monthly until the end of the 12 month sampling period. For each manure application timing, this sampling schedule resulted in an annual total of c.30 sampling days starting from the day of the application. Measurements were taken over 12 months to follow IPCC good practice guidance and so that the results were directly comparable to the IPCC 2006 methodology default emission factor. Nitrous oxide fluxes from the five replicate chambers per plot were averaged. Cumulative fluxes were calculated using the trapezoidal rule to interpolate fluxes between sampling points.
References:
Chadwick, D.R., Cardenas, L., Misselbrook, T.H., Smith, K.A., Rees, R.M., Watson, C.J., McGeough, K.L., Williams, J.R., Cloy, J.M., Thorman, R.E. & Dhanoa, M.S. (2014). Optimizing chamber methods for measuring nitrous oxide emissions from plot-based agricultural experiments. European Journal of Soil Science 65, 295-307.
(IPCC, 2000). Good Practice Guidance & Uncertainty Management in National Greenhouse Gas Inventories. Penman, J., Kruger, D., Galbally, I., Hiraishi, T., Nyenzi, B., Emmanul, S., Buendia, L., Hoppaus, R., Martinsen, T., Meijer, J., Miwa, K. znd Tanabe, K. (Eds). IGES, Japan.
Smith K.A., Dobbie K.E., Thorman R., Watson C.J., Chadwick D.R., Yamulki S. & Ball B.C. (2012). The effect of N fertilizer forms on nitrous oxide emissions from UK arable land and grassland. Nutrient Cycling in Agroecosystems 93, 127-149.Publication Date: